1. Field of the Invention
The present invention relates to a flat display in which an auxiliary capacity is connected to a pixel displaying switching element and a method of manufacturing the display, and it relates, for example, to an active matrix liquid crystal display.
2. Related Background Art
A liquid crystal display, provided with great advantages such as a high image quality, thinness/lightweight, and low power consumption, is broadly utilized in a notebook-size personal computer, a portable electronic apparatus, and the like. Particularly, in recent years, the liquid crystal display has been intensively developed/researched in which a thin film transistor (hereinafter referred to as TFT) by a polycrystalline silicon with a high mobility is used in a pixel switching element.
FIG. 1 is a top view showing a structure of the liquid crystal display using this type of TFT, and FIG. 2 is a sectional view along line A—A of FIG. 1.
A method of manufacturing the liquid crystal display of FIG. 1 will briefly be described hereinafter. After forming a semiconductor layer 2 of polycrystalline silicon on the top surface of a glass substrate 1, and forming a gate insulating film 4 to cover the semiconductor layer 2, a gate electrode 5 as a first wiring layer is formed on the top surface.
A pixel electrode 19 and an auxiliary capacity electrode 3 are connected to TFT for displaying a pixel. The auxiliary capacity is structured such that the gate insulating film 4 is held between the auxiliary capacity electrode 3 formed by the semiconductor layer 2 and an auxiliary capacity feeder 6 formed on the same layer as that of the gate electrode 5.
For the TFT shown in FIG. 1, since polycrystalline silicon is used as a material of the semiconductor layer 2, field-effect mobility is high, and even with individual miniaturized TFTs, a sufficient drive ability can be obtained. Therefore, when this type of TFT is used to constitute the active matrix liquid crystal display, aperture ratio and luminance can be enhanced, and power consumption can be reduced.
Moreover, since this type of TFT has a high field-effect mobility, it is also possible to form a drive circuit such as a shift register for controlling TFT operation on the same glass substrate as that of an image display area. Therefore, it is unnecessary to separately dispose a TFT driving substrate, an external circuit can be simplified, and manufacture process and cost can be reduced.
However, in the liquid crystal display of FIG. 1, because of surface property of the auxiliary capacity electrode 3, mixture of foreign particles in the course of manufacture, and the like, insulating property of the capacity insulating film (gate insulating film) 4 of the auxiliary capacity becomes insufficient, a defect of short-circuiting the pixel electrode 19 and auxiliary capacity feeder 6 occurs, and manufacture yield is deteriorated.
When such defect occurs, the corresponding pixel is fixed to a certain potential, and a constantly lit pixel defect occurs. Moreover, since a direct-current voltage continues to be applied between opposite electrodes, a liquid crystal composition contained in a liquid crystal layer corresponding to a pixel area is deteriorated, and reliability is also deteriorated.
As one technique of repairing this pixel defect, there is proposed a technique of irradiating, with a laser beam, an auxiliary capacity electrode portion in which a short-circuit defect occurs to cut this portion, thereby electrically cutting the above portion from the pixel electrode. In this case, the repaired pixel is influenced by a parasitic capacity between a signal line and the pixel electrode, but is improved to obtain a semi-lit state.
However, in a wiring BM structure as a pixel structure for realizing a high aperture ratio, since a wiring portion is vertically superposed on the pixel electrode, by cutting a part of the wiring portion with a laser beam, a new short-circuit defect possibly occurs by the laser beam.
In order to avoid such possibility, it is necessary to connect the auxiliary capacity electrode to the switching element beforehand via the wiring to be cut, and to detect and cut off a short-circuit place before forming the pixel electrode.
However, a finding ratio of the short-circuit place is not 100% in a state of array substrate, and after completing the array substrate, the short-circuit place newly found after the substrate is placed onto an opposite substrate cannot be repaired.